FIXED
I have tested all my region (in world/region). If exists r.0.-1.mca from World 1.8, the server interrupted the connect to me and my friends.
If the server 15w31a created r. 0.-1, he is working.

Informations:
Operating system: Windows 8.1
Java: v1.8.0_51 (64 bit)
Minecraft-World: 1.8 has created.
Minecraft-Server: minecraft_server.15w31a.jar
Server-Log:
[12:02:55 INFO]: Starting minecraft server version 15w31a
[12:02:55 INFO]: Loading properties
[12:02:55 INFO]: Default game type: SURVIVAL
[12:02:55 INFO]: Generating keypair
[12:02:56 INFO]: Starting Minecraft server on *:25565
[12:02:56 INFO]: Using default channel type
[12:02:56 INFO]: Preparing level "world"
[12:02:56 INFO]: Preparing start region for level 0
[12:02:57 INFO]: Preparing spawn area: 27%
[12:02:58 INFO]: Preparing spawn area: 62%
[12:02:59 INFO]: Done (3,348s)! For help, type "help" or "?"
[12:03:11 INFO]: UUID of player PLAYERNAME is CODE
[12:03:11 INFO]: PLAYERNAME[/LOCALIP] logged in with entity id IDCODE at (267.3855144615776, 67.8039999961853, -290.0964607589612)
[12:03:11 INFO]: PLAYERNAME joined the game
[12:03:13 INFO]: PLAYERNAME lost connection: TranslatableComponent{key='disconnect.genericReason', args=[Internal Exception: java.io.IOException: An existing connection was controlled by software
canceled by the host computer.], siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null, insertion=null}}
[12:03:13 INFO]: PLAYERNAME left the game

Minecraft-Screen-Error:
Internal Exception: io.netty.handler.codec.DecoderException:
com.google.gson.JsonSyntaxException:
com.google.gson.stream.MalformedJsonException: Use JsonReader.setLenient(true) to accept malformed JSON at line 1 column 2